Fuser rolls used in electrostatographic imaging systems generally comprise a metal core cylinder coated with one or more elastomer layers. Conventional fuser roll core cylinders are relatively thick walled aluminum alloy cylinders. Such thickness has been desired in order to provide strength and durability as the fuser roll presses against the nip of the adjoining compression roll. For a 35.00 mm outside diameter fuser roll core, a thickness of 5.5 mm is fairly standard. Similar dimensions are common in office and production printing systems capable of imaging more than 50 pages per minute. One drawback to such relative thickness is that thicker walls make the cylinder more massive. Since a typical fuser must attain a fusing temperature of approximately 150 C, significant power and time are required to heat and maintain the fuser at fusing temperatures. For conventional fuser cores of about 5.5 mm thickness, warm-up time lasts from about 7 to about 30 minutes.
In order to save energy and to shorten warm-up times, it would be desirable to reduce the wall thickness of fuser cylinder cores as much as possible. Experience indicates, however, that simply thinning cylinder walls creates problems in the end region of the cylinder. In particular, weakness and cracking results at the end if conventional drive slots are machined into the fuser core cylinders. Drive slots are used as part of the system to rotate fuser cylinder cores. As shown in FIG. 1, rotation is generally caused by mating a core cylinder 10 snugly with a drive gear 11. Mating occurs by driving key 15 into slot 14. Because heating lamps need to be inserted into the fuser roll core subsequent to mating of drive gear 11 to cylinder 10, the inside diameter of drive gear 11 forms a sleeve 12 that slips over core cylinder 10 in the manner shown. Key pin 15 protrudes inwardly from sleeve 12 to engage slot 12. Another reason that sleeve 14 slips over cylinder 10 rather than into cylinder 10 is that drive gear 11, together with sleeve 12, is generally made of rigid plastic. Such plastic has a different co-efficient of expansion than the metal of cylinder 10. Thus, if sleeve 12 protruded inside of cylinder 10, the metal of cylinder 10 would expand at a rate greater than the plastic of drive gear 11 during fusing and thereby create undesirable looseness between drive gear 11 and cylinder 10.
It would be desirable to produce a durable thin-walled core fuser cylinder that enables energy efficiency and fast warm-up times while meeting or exceeding specifications for durability and imaging performance.
One embodiment of a thin-walled fuser roll assembly of the present invention is a thin-walled fuser roll core assembly, comprising: a metallic core cylinder having a wall thickness between about 0.5 millimeters and about 2.0 millimeters, an end region, and having an axial and a radial direction; a drive gear having an internal diameter sleeve for fitting over an end of the core cylinder and a key for forcing rotation of the core cylinder; a keyway in the end region of the core cylinder for receiving the drive gear key, said keyway having a terminus; a means for redirecting axial oriented stress at the terminus of the keyway to a radial direction.
Another embodiment of the present invention is an electrostatographic imaging system, comprising: a thin-walled fuser roll assembly, comprising: a metallic core cylinder having a wall thickness between about 0.5 millimeters and about 2.0 millimeters, an end region, and having an axial and a radial direction; a drive gear having an internal diameter sleeve for fitting over an end of the core cylinder and a key for forcing rotation of the core cylinder; a keyway in the end region of the core cylinder for receiving the drive gear key, said key way having a terminus; a means for redirecting axial oriented stress at the terminus of the keyway to a radial direction.
Yet another embodiment of the present invention is a process for fusing toner to a copy sheet, comprising: for a period less than about one (1) minute, pre-heating a thin-walled fuser roll comprising core cylinder walls between about 0.5 millimeters and about 2.0 millimeters thick wherein a redirecting means redirects axial oriented stress at the terminus of an axial keyway formed in the thin walls to a radial direction; moving a copy sheet into engagement with a nip formed by the fuser roll and a pressure roll; and driving rotation of the fuser roll with a drive gear having an internal diameter sleeve fitting over an end of the core cylinder and a key for engaging the keyway of the core cylinder, thereby moving the paper through the nip.